Malignant gliomas are diffuse infiltrative growing tumors with a poor prognosis despite treatment with a combination of surgery, radiotherapy and chemotherapy. It has been shown recently that complete tumor resection improves the survival time significantly. Hypericin, a component of St. Johns Wort, is one of the most powerful photosensitizers in nature. The aim of the present study was to investigate accumulation of hypericin in intracerebral implanted malignant glioma in vivo. Rats underwent stereotactic implantation of C6 glioma cells. After intravenous administration of hypericin (5 mg per kg body weight), accumulation of the compound was studied in tumor, the infiltration zone surrounding the tumor and healthy brain (contralateral hemisphere) by fluorescence microscopy between 0 and 48 h after injection. Results were compared by one-way analysis of variance. For post hoc pair-wise comparison the Tukey-Kramer HSD test was used. Accumulation of hypericin was significantly higher in C6 glioma as compared to normal tissue. Maximum hypericin uptake was achieved at 24 h after injection. Ratios of fluorescence intensity between tumor and normal tissue as well as infiltration zone and normal tissue of about 6.1:1 and 1.4:1 were found. Considering tissue auto-fluorescence, fluorescence ratios of about 19.8:1 and 2.5:1 were calculated, respectively. Therefore, hypericin seems to be quite an effective fluorescence marker for the detection of glioma in vivo. To the best of our knowledge, the present study demonstrates for the first time that hypericin accumulates selectively in intracerebral implanted C6 glioma in vivo after systemic (intravenous) administration.